This invention relates to heat exchange apparatus and particularly such apparatus useful for ventilation air exchange in buildings.
It is well known to provide heat exchangers which allow heated air to be drawn from a room or building for exhaust to the exterior and to pass the air through a heat exchange block which defines a second path for incoming air whereby the outgoing air warms the incoming air to avoid undue heat loss from the building. The heat exchange block provides a plurality of layers or sheets of material which act to separate the two flows of air which provide the necessary heat exchange.
A number of problems exist with this type of unit, particularly when used for ventilation for a building used in livestock confinement. In fall and in winter, such a building is characterized by moderate temperature (60.degree. F. to 70.degree. F.) and high humidity. The temperature is achieved and maintained both biologically (through metabolism of feed) and by mechanical heat sources. The high humidity is the direct result of animal metabolism, density of confinement and evaporation of wastes. The humidity is highly corrosive in some types of livestock confinement operations and oxygen consumption in such environments is very high. Therefore, the primary environment management problem in livestock confinement operations has been meeting the high required rates of ventilation for oxygen replenishment and de-humidification while not giving up the moderate temperature conditions and while minimizing the cost of fuels necessary to maintain the temperature conditions.
Traditionally, confinement livestock operators have had two responses to these thermally contradictory circumstances, either they shut down for the coldest part of the year or they ventilate and heat at the same time at a great cost. There has been therefore a substantial need for a cheap, simple and efficient air-to-air heat exchanger to overcome this problem. The heat exchanger, operating across a temperature spread of as much as 100.degree. F. and very high humidity differentials must achieve efficiencies of heat transfer as much as 60% to 90%. At lower efficiencies, significant temperature drops in the barn may be experienced. At these higher efficiencies, the amount of heat recovered from the outgoing air is sufficient that it tends to cause freezing in the exhaust part of the exchanger. There has been a need therefore to include a defrosting mechanism which enables the use of the higher efficiencies which are necessary to maintain the temperature within the barn.
A further problem particularly relevant to the above conditions is the very high corrosiveness of the exhausted gases. This corrosiveness can have very serious effects upon any metal parts within the heat exchanger.
A yet further problem is that the incoming air must be circulated or distributed within the room, particularly bearing in mind the high density of confinement and the high requirement for oxygen caused thereby. It is possible to provide such distribution of the air by additional duct work within the building but this substantially increases cost and complexity, bearing in mind that many buildings may be of a structure not suitable to receive such duct work.